Defense Intelligence Reference Document Pulsed High-Power Microwave Source Technology

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One major use of HPM by the military is for electronic attack, or what is
referred to by the media as an "ebomb." HPM sources developed for this
purpose provide peak powers in excess of 10 gigawatts. The goal of such a
weapon is to disable communications and computer systems prior to any troop
movements and render the enemy unable to stage a response. The technology
used to drive such sources has its roots in pulsed power, and for narrowband
sources requires the use of tools that have been developed in the plasma
physics community. Reliance on microprocessors that have an increasing
density of circuits packaged onto each chip makes such systems ever-more
vulnerable to HPM effects. As an example of the possible effects of HPM
weapons, on 28 May 2001, a U.S. Commanche helicopter, flying in New York
state while performing tests involving HPM weapons, was reported to have
generated a low-level energy pulse that disrupted the Global Positioning
System devices used to land commercial aircraft in Albany.
The use of this type of weapon can be based on several scenarios, depending
on the asset it will be used against. Sometimes, it may only be necessary to
upset a data bus transfer to produce a success; other times, success may not
be so simple. Some of the kill mechanisms obtained from microwave weapons
include semiconductor overheating or burnout, arc generation, computer
upsets, voltage induction into sensitive circuits, display upset, and overvoltage
in discrete components. The asset to be neutralized will often determine the
specific type of microwave source to be used; for example, assets with slots
designed for communications purposes may be most vulnerable to narrowband
HPM of a specific frequency, while assets with several computers linked by a
communications bus may be more vulnerable to ultrawideband (UWB) pulses
of a specific pulse repetition rate (PRR). Often, the variety of EM radiation that
would be most effective is not obvious, and therefore several must be
evaluated.
If EM radiation is able to penetrate a target, the issue then becomes the
susceptibility of the many semiconductor devices, which make up the various
circuits of the target. Failures in semiconductors owing to thermal effects
occur when junction temperatures are raised above 600° Kelvin. Since thermal
energy diffuses through the semiconductor, failure mechanisms depend on the
microwave pulse duration. If the pulse duration is short compared with
thermal diffusion times, then the temperature increases in proportion to the
deposited energy. Pulse durations (t) shorter than about 100 nanoseconds fall
into this regime, and the threshold power for damage varies as 1/t.
Experimental testing has shown that for pulse durations between 100
nanoseconds and 10 microseconds, the power required for damage scales as
1/t11 2 • And for pulses longer than 10 microseconds, a steady state in which the
thermal diffusion rate equals the rate of energy deposition and temperature is
proportional to power, resulting in a constant power requirement for damage.
In this case, the power requirement scales as t. The consequence of these
scaling factors is that short pulses require very high power but little energy,
while very long pulses require large amounts of energy but little power. This
analysis results in a vast range of HPM sources capable of damaging
semiconductor devices. The above applies to single-shot pulse durations, but if
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